1. Field of the Invention
The present invention relates generally to a parameter determining method suitable particularly for use in a correcting means for automatically correcting a portrait image.
2. Related Background Art
Digital images have hitherto been subjected to a variety of image processing such as adjusting saturation, a color tone, a contrast and gradations. It is general in the prior arts that when executing the image processing, an operator having knowledge specialized in the images utilizes specialized or dedicated pieces of software and employs the empirical knowledge, thereby obtaining a preferable image on a trial-and-error basis in a way that checks a result of the image processing on a monitor screen of a computer, and so on.
Over the recent years, a wide spread of digital cameras has advanced as if towed by the spread of the Internet. This is because a result (data) acquired by photographing with the digital camera is easy-to-read file formatted data on a computer. This facilitates such an operation that, for example, an image captured by the digital camera is stored on a server on WWW (World Wide Web) and is opened in public to a third party.
Another fact is that the spread of the digital cameras induces a rise in digital image data around users who have been unfamiliar so far with the image (data).
The users of the digital camera would be considered insufficient of the knowledge about the camera though they have in-depth knowledge about the computer rather than those who have so sufficient knowledge about the conventional analog cameras as to have a good capability of using these analog cameras.
Therefore, the images captured by the digital camera are not invariably images captured under preferable conditions. Even an image captured under unpreferable conditions can not be invariably discarded if a content of this image is important to a photographer. For this reason, there is a desire for an image correcting method capable of obtaining a proper image even from the image captured under the unpreferable conditions.
Further, as described earlier, it appears to be preferable that the image correcting method functions automatically or semi-automatically in terms of such points that the users are not invariably those who are familiar with the cameras or the image (data) and that the image data increases.
Further, in the case of a portrait photo, a main emphasized area is a face of a person as an object, and it is preferable that the face area exhibits proper brightness. Hence, if not photographed with the proper brightness, it is expected to be preferable that the image is so corrected as to be adjusted to the suitable brightness.
As for the brightness adjustment described above, according to the great majority of known image correcting methods, an image brightness distribution state is examined, and several percents of levels from the bright side and from the dark side are set as a highlight point, a shadow point, etc. Then, major processing is that a level extension is conducted so that the highlight point becomes approximately a maximum value of the brightness or the shadow point becomes approximately a minimum value of the brightness, and that a γ-correction is executed based on average luminance of the whole image.
The conventional image correcting methods are, however, methods that emphasize separately only the brightness of one face area. Namely, the conventional image correcting methods did not, though capable of adjusting the brightness of each of the face areas in case that a photo generally contains a plurality of faces of persons, provide any means for determining one correction parameter value by integrating a plurality of correction parameter values of the face areas.